This invention relates to paperboard containers of the type suitable for liquid food products such as milk and fruit juices, and more particularly relates to a paperboard container for liquid food products which exhibits improved upright standing stability when filled.
Liquid tight containers suitable for distributing consumer quantities of liquid food products are frequently fabricated from paperboard sheets coated with a film of heat sealable, waterproof thermoplastic such as polyethylene, polyvinyl chloride or polypropylene. These plastic coated sheets are cut into blanks which are first folded into four-sided tubes and then closed by a lap fold of bottom panels extending integrally from the four side walls. While the plastic film coating is still hot and tacky, the bottom wall lap panels are fused together by a bottom sealing die.
Paperboard containers for liquid food products have an inherent instability due to the pressure exerted on the walls by the fluid, particularly the bulging effect of the fluid on the bottom. The degree of bulging is a function of the stiffness of the board, i.e., stiffer board exhibits less bulging. Thus, one way to address a bulging problem is to use a stiffer board. However, increasing the stiffness often combs at the cost of other board properties and a stiffer board is generally more difficult to fold and assemble into the erected container. Stiffer boards also tend to be more expensive, which drives up the cost of the container.
These and other problems have limited progress toward achieving an economical carton bottom construction with a minimum of center bulging and improved stability.
It is therefore an object of the present invention to provide a method of forming lapped bottom panels of a paperboard fluid carton into a support surface of improved stability.
Another object of the present invention is to provide a paperboard carton bottom which is stiffened against center bulging from fluid content pressure.
A further object of the invention is to provide an economical paperboard carton bottom construction of improved stability.